Floristic composition, diversity and structure of the forest communities in the Kouilou Département, Republic of Congo

Abstract:

The objectives of the study were to classify, describe and map the forest
communities in the study area and to investigate possible gradients in plant diversity. The
study area comprised approximately 166 000 ha in the Kouilou Département, Republic of
Congo, a section of land targeted for extensive future development. In total 156 forest sample
sites were surveyed using the Braun-Blanquet method of phytosociology. Diversity of each plant
community was expressed in terms of species richness; Shannon-Wiener index; exponent of
Shannon-Wiener index; evenness; Fisher's alpha; Simpson’s index; and inverse Simpson index.
Eleven plant communities were described and mapped at a much finer scale than has been done
previously. The communities were arranged along two gradients: a degraded – relatively intact
gradient and a wet – dry gradient. The least degraded communities, and consequently those
with the highest conservation value, were the swamp forests and the okoumé forest. Overall,
the values reported for the diversity parameters in the current study were within the range
reported for other tropical forests in Central Africa. The study revealed a gradient between the
coast (west) and the Mayombe mountain range (east) in plant diversity linked to topography
and climate with plant diversity lowest at the coast. Furthermore, plant diversity was
negatively related to the distance to human infrastructure. The forest communities appear to be
fairly resilient to past anthropogenic disturbances, however, there is no historical analogue to
the more severe types of forest destruction associated with some of the future developments
anticipated, such as mechanized logging or mining.